Hubble Spots Colossal 10-Sided “Decagon” Storm at Saturn’s South Pole
Saturn’s famous north-pole hexagon finally has a southern rival—and it is even bigger.
Astronomers have discovered an enormous, 10-sided wave pattern swirling through the icy ammonia clouds over Saturn’s south pole. First spotted by the Hubble Space Telescope in 2023, the spinning, meandering decagon challenges what scientists thought they knew about the ringed planet’s geometry-defying weather systems.
The findings, published Wednesday in the journal Science Advances, prove that the massive hexagonal storm system discovered in the 1980s is not an isolated anomaly.
A Geometric Mystery Hidden in the Dark
The newly discovered jet stream formation eluded earlier observations, leading researchers to suspect the bizarre atmospheric phenomenon formed between 2017 and 2023. During this period, Saturn’s south pole was tilted away from Earth, keeping the developing storm hidden from view in the darkness of deep space.
It is a meteorological monster. The decagon could still be evolving, and a single side of the 10-sided polygon already exceeds 10,000 miles (16,700 kilometers) in length.
According to lead author Agustin Sanchez-Lavega of the University of the Basque Country, the breakthrough demonstrates that Saturn’s previously discovered northern storm system is part of a larger planetary dynamic. The finding shows “the ‘unique’ hexagon is not as extraordinary as we thought,” Sanchez-Lavega said in an email.
Hexagon vs. Decagon: A Tale of Two Poles
While all planets with atmospheres in our solar system experience wave-spawning disturbances, Saturn is the only one that churns them out as distinct, straight-lined polygons.
Though both of Saturn’s polar storms sit on jet streams, they behave very differently. The northern hexagon—first spied by NASA’s twin Voyager spacecraft more than 40 years ago—is practically stationary. In contrast, the newly discovered southern decagon appears more unstable and migrates eastward at a leisurely 6 mph (10 kph).
“Saturn still has the ability to surprise us,” said Leigh Fletcher of the University of Leicester. Fletcher contributed to the study by measuring the winds inside the decagon using the European Southern Observatory’s Very Large Telescope in Chile.
By studying these twin formations on opposite ends of the gas giant, scientists hope to unlock the broader mechanics of weather patterns on massive planetary bodies. Sanchez-Lavega noted that the team is also investigating whether these straight-lined formations share a physical connection to the cyclonic clusters found on Jupiter, which also arrange themselves in polygonal shapes.
What Happens Next?
The immediate question for astronomers is how long this new decagon will survive.
The northern hexagon has been visible to spacecraft for over four decades, outlasting a full Saturnian year (which equals 30 Earth years). Because the southern decagon is more unstable, its lifespan remains a total mystery. Improving views of Saturn’s southern hemisphere over the next few years should allow astronomers to capture sharper details and track its evolution.
“This is a highly interesting phenomenon that appears to be unique to Saturn, and we want to know why,” Sanchez-Lavega said, adding a note of scientific caution regarding its future: “For the time being, all I can confirm is that the decagon is still there.”